No sound on blue ray disc

Hello,
have a blue ray disc player ,Panasonic ,will play sound on some BR disc but can only get sound on others with the commentary i`m playing through a panasonis sound system with an optical link between the BR player and the sound system. any ideas.

Additionally connect the Audio left and right outputs from the BR player to the sound system, and see what that does for you.

Also this can happen from using a cheap HDMI cable, Sams Club, and Home Depot, have some very high quality HDMI cables for reasonable prices, its important that the cables are shielded.

However there are some brand sound systems that don't transfer the sound over the HDMI cable, requiring my first suggestion to be implemented, but that would mean you wouldn't be getting sound playback of any kind.

So either connect the audio outputs or get a better quality HDMI cable, you could also actually have a high quality HDMI cable with a factory defect?

Hope this helps you!